The proposed research concerns our interest in the genetic control of immunoglobulin synthesis. We have chosen to study this system in rabbits for several reasons, among them including availability of materials, ease in genetic handling (breeding, etc.), a large collection of factual data already available and our own expertise from studies during the past five years. Also recent results suggest that several concepts concerning regulation of immunoglobulin synthesis, particularly in the rabbit system, need re-evaluation or re-interpretation. Because of the close phylogenetic relationship of the present-day lagomorphs, we have included in our model system the immunoglobulins of the hare (Lepus) and cottontail rabbit (Sylvilagus). Our overall objective therefore is to study further rabbit immunoglobulin allotypes as aids in monitoring the genetics and evolution of immunoglobulins in general. It is anticipated that these efforts will contribute toward a better understanding of the genetic and chemical basis of antibody diversity.